Optimization of dead space in pistonless compressors

ABSTRACT

A method for operating a pistonless compressor, which serves the purpose of compressing a gaseous medium, in particular a cryogenic medium and in the cylinder of which a liquid column is moved up and down, is described.

CROSS REFERENCE TO RELATED APPLICATIONS

The present application claims priority from German patent application DE 1020060143, filed Mar. 28, 2006, and Patent Cooperation Treaty application PCT/EP2007/001912 filed Mar. 6, 2007.

BACKGROUND OF THE INVENTION

The invention relates to a method for operating a pistonless compressor, which serves the purpose of compressing a gaseous medium, in particular a cryogenic medium and in the cylinder of which a liquid column is moved up and down.

The term “pistonless compressor” is to be understood to be a compressor and a device for compressing a gaseous medium, respectively, as it/they is/are disclosed in PCT patent application PCT/EP2005/008370. Such devices are identified as “pistonless compressors”, because a liquid column instead of a fixed piston is moved up and down therein. For a short time, ionic liquids are also being used as liquids for such compressors. They have a plurality of advantages, as they are also disclosed in the afore-mentioned PCT patent application. By means of the citation of PCT patent application PCT/EP2005/008370, the disclosure content thereof is to be integrated into the disclosure content of the instant patent application in its entirety. Pistonless compressors serve the purpose of compressing hydrogen, oxygen, helium, nitrogen, argon, etc., in particular.

With conventional compressors—thus compressors, where a common piston is used—the problem existed until now that the piston was capable of approaching the theoretically possible uppermost dead center only up to a certain point. As a consequence, a so-called dead space remains in the region of the cylinder head. The compressed medium, which is present in this dead space, relaxes during the inlet stroke to the suction pressure. Consequently, the delivery rate of the compressor is reduced. Furthermore, this gas must be compressed again in response to the proximate compression cycle. As a consequence, in turn, the specific compression energy rises as well.

Adherence to a dead space volume, however, is absolutely necessary because it must be avoided that the piston moving upwards touches the cylinder head. This requirement must also be able to be fulfilled when a considerable thermal change of the system piston/cylinder takes place.

SUMMARY OF THE INVENTION

Fundamentally similar considerations apply for the so-called pistonless compressors. In a schematized sectional view, FIG. 1 illustrates the upper region of a cylinder 1′ of a pistonless compressor. A liquid column 2′ is moved up and down in the cylinder 1′ of said pistonless compressor. Once the liquid column 2′ has reached its upper dead center, a dead space 3′ remains. A supply line 4′ as well as a discharge line 5′, which serve the purpose of supplying and discharging the gaseous medium to be compressed into the cylinder 1′ are furthermore illustrated in a schematized manner.

With pistonless compressors, the thermal change of the piston medium is not important, because the respective actual state of the liquid column 2′ is known. Consequently, the dead space 3′—as compared to a common compressor—becomes smaller. However, to prevent an excess delivery of the liquid and piston medium, respectively, into the discharge line 5′, a defined dead space must furthermore be maintained. The disadvantages described in context with common compressors are thus still present, albeit to a lesser extent.

As illustrated in the figure of the afore-mentioned PCT patent application PCT/EP2005/008370, a separator unit is assigned to the discharge line of the pistonless compressor. A separation of the operating liquid, which is undesirably carried along via the compressed medium, is possible in the separator. Presently, however, such separator units only serve the purpose of separating liquid, which was undesirably carried along, out of the compressed media flow. They are thus dimensioned for comparatively small separation quantities.

It is the object of the instant invention to specify a generic method for operating a pistonless compressor, which avoids the afore-mentioned disadvantages, in particular increases the delivery rate of a pistonless compressor and minimizes the specific compression energy.

To solve this object, a generic method for operating a pistonless compressor is proposed, which is characterized in that an excess delivery of a part of the liquid is permitted during the compression cycle.

Further advantageous embodiments of the method according to the invention for operating a pistonless compressor are characterized in that

-   the liquid delivered in excess is separated from the compressed     medium and -   the liquid delivered in excess separated from the compressed medium     is guided back into the cylinder or cylinders of the compressor.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic of the upper region of a cylinder of a pistonless compressor.

FIG. 2 is a schematic of the upper region of a cylinder of a pistonless compressor showing a discharge line for a separator unit.

DETAILED DESCRIPTION OF THE INVENTION

A separation of the liquid delivered in excess from the compressed medium is advantageous or required in particular when the liquid delivered in excess represents an undesired contamination in a subsequent process, to which the compressed medium is supplied. When ionic liquids are used as operating means, a separation and return of the liquid delivered in excess seems to be sensible for cost reasons as well. Furthermore, the “loss” of the liquid quantity delivered in excess, among other things, can also be accepted, in particular when a replacement of the liquid quantity delivered in excess with new operating liquids is required or desired.

The method according to the invention for operating a pistonless compressor as well as further embodiments thereof, which represent objects of the dependent patent claims, shall be specified in detail below by means of the exemplary embodiment illustrated in FIG. 2.

As already shown in FIG. 1, FIG. 2 also shows a schematized sectional view of the upper region of a cylinder 1 of a pistonless compressor. Provision is now made in the discharge line 5 for a separator unit 6, in which the liquid delivered in excess—illustrated in FIG. 2 in the discharge line 5 in a diagonally hatched manner—is separated from the compressed media flow, which is pushed out of the cylinder 1 via the line 5. The compressed media flow, which is freed from this liquid delivered in excess, is subsequently removed via the line 8, while the liquid delivered in excess, which is separated in the separator unit 6, is removed via the line 7.

As compared to common separator units, the separator unit 6 is designed for a greater phase contamination, because the undesired excess delivery must be separated in addition to the undesired introduction of the (ionic) operating means into the compressed media flow. The separator unit can separate the two-phase mixture (medium/(ionic) operating means) with the help of the gravitation, the coriolis force, an electric field or a combination of these release forces.

According to the invention—in completely departing from the teaching of the known state of the art—an excess delivery of a part of the liquid 2 into the discharge line 5 is permitted and enforced, respectively, during the compression cycle. By means of controlling the liquid column 2, a defined liquid quantity can hereby be delivered in excess into the discharge line 5. By using the method according to the invention it is attained that no dead space volume remains within the cylinder 1, whereby the desired, afore-mentioned advantages can be realized.

Applications where a separation of the liquid 2 delivered in excess out of the compressed media flow can be omitted. As a rule, however, provision is made for a separator unit 6 for being able to realize the afore-mentioned separation. If a separation 6 is not necessary, it must be ensured, however, that the liquid quantity 2 in the cylinder 1 delivered in excess is replaced.

In a further embodiment of the method for operating a pistonless compressor according to the invention, it is proposed that the liquid 7, which is delivered in excess and which is separated from the compressed medium, is returned back into the cylinder or the cylinders 1 of the compressor.

This embodiment of the method according to the invention is sensible in particular when the liquid is a comparatively expensive ionic liquid, for example.

As compared to the methods belonging to the state of the art, the method for operating a pistonless compressor according to the invention has a higher delivery rate and furthermore requires a lower specific compression energy. 

1. A method for operating a pistonless compressor, which serves the purpose of compressing a gaseous medium, in particular a cryogenic medium and in the cylinder of which a liquid column is moved up and down, characterized in that an excess delivery of a part of the liquid is permitted during the compression cycle.
 2. The method according to claim 1, characterized in that the liquid delivered in excess is separated from the compressed medium.
 3. The method according to claim 2, characterized in that the liquid delivered in excess and separated from the compressed medium is returned into the cylinder or cylinders of the compressor. 